1. Field of the Invention
The present invention relates to a yarn supply apparatus for knitting machines, and more particularly to a yarn supply apparatus for knitting machines having a yarn supply drum for scraping nap out of yarn and the circumferential surface of the yarn supply drum.
2. Description of Related Art
As known, a circular knitting machine comprises several hundred of yarn supply drums. The yarn can be drawn from a bobbin through the guiding of yarn guides to the knitting machine for knitting. However, it is inevitable for nap to be accumulated on the yarn supply drums and/or yarn guides when in high speed operation. It is found that nap is subject to being accumulated on the bottom of the yarn supply drum. It is known that a yarn consists of a plurality of twisted filaments. It is common for any single filament of the yarn to be broken in operation. As a result, yarn supply becomes difficult when such accumulation worsens. This is a problem that bothers many persons skilled in the art.
U.S. Pat. No. 4,793,565 discloses an apparatus for solving such a problem. As shown in FIG. 1, a free ring 27 is provided on the circumferential surface of the lower part of the yarn supply drum. The ring 27 is able to scrape the accumulated nap out of the lower part 24 of the yarn supply drum by means of vibration. However, the ring 27 is a circular shape, and the surface of the yarn supply drum is a cylindrical shape, and the lower section 23 of the yarn supply drum is a conical body. The yarn 8 is in tangent contact with a plurality of pins. The yarn 8, which is drawn out of the lower part 24 of the yarn supply drum, is inclined at an angle about 15 degrees with respect to horizontal. It is known that the contact of a circumference with a straight line is a point. This means that the contact area between the yarn 8 and the circumferential surface of the drum is very small. Further, it is not possible to scrape nap nor stop nap from being accumulated on the lower part 24 and the ring 27 because the lower section 23 is a conical body as mentioned above. Such design is unsatisfactory for the fulfilment of the requirement of high speed operation. Worse, it can impede the operating procedure.
Thus, it is desirable to provide a yarn supply apparatus for knitting machines without the drawbacks of the prior art.